The field of the present invention relates to the delivery of energy impulses to bodily tissues for therapeutic purposes, particularly the use of implanted electrical stimulators. The disclosed methods and devices may be used to treat discogenic lower back pain, by selectively stimulating nerves that innervate a posterior longitudinal ligament and/or the adjacent outer posterior annulus fibrosus of a lumbar disc.
More specifically, the present invention is directed to methods and devices for the treatment of chronic lower back pain that may result from a degenerated or injured intervertebral disc, or paraspinal-mediated low back pain. Electrodes, along with a pulse generator that is connected to the electrodes, are used to deliver electrical impulses to nociceptive and/or other nerves located within the posterior longitudinal ligament of the lumbar spine and the posterior annulus fibrosus of the intervertebral disc(s) that lies adjacent to the posterior longitudinal ligament. According to the invention, the electrical stimulation in this region may reduce back pain in a patient reversibly, adjustably, and with almost complete coverage of the pain-generating region, for example, by interfering with or modulating afferent pain signals to the brain that originate in those nerves. Alternatively, if the reversible electrical stimulation is unsuccessful in alleviating the back pain, electrical stimulation parameters may be selected so as to irreversibly damage the ability of the nerves to send pain signals to the brain, using non-thermal irreversible electroporation. In a different embodiment, the device may be used to relieve pain in the patient by irreversibly damaging nerves in the posterior longitudinal ligament and/or posterior annulus fibrosus by joule heating and/or by dielectric heating of proteins, wherein a thermal insulator covers substantially all of the cauda equina or thecal sac, thereby shielding the cauda equina or thecal sac from the heat that could cause damage.
The disclosed methods involve the implantation of electrically stimulating electrodes within the anterior epidural space, adjacent to the posterior longitudinal ligament (PLL) of the lumbar spine. Such implantation is disclosed in detail below, but for purposes of providing background information, the relevant anatomy of the spine and vertebrae will first be summarized and illustrated in FIGS. 1 to 4.
Proceeding from the neck to the tailbone, there are 7 cervical (neck) vertebrae (C1-C7), 12 thoracic vertebrae (T1-T12), and 5 lumbar vertebrae (L1-L5). This is followed by the 5 sacral and coccyx (tailbone) vertebrae, which are inserted like a wedge between the two hip bones. The present invention is concerned primarily with the lumbar vertebrae L3 to L5, although it is understood that the invention may be adapted for use in other vertebrae as well, for example, the lumbar vertebrae L1 to L3, or the sacral vertebrae.
The vertebral column comprises bony vertebral bodies that are separated by cartilaginous intervertebral discs. A primary function of the vertebral column is to provide mechanical support for the body. The intervertebral discs provide a cushion between the vertebral bodies, absorbing some of the axial load and also facilitating motion within the vertebral column. Each disc contains a soft gel-like center (the nucleus pulposus), which is constrained radially by an elastic outer band, the annulus fibrosus. Each vertebral body articulates with its neighboring vertebral body above and below, which allows for some degree of flexion, extension, and rotation [HUMZAH M D, Soames R W. Human intervertebral disc: structure and function. Anat Rec 220(4,1988):337-56].
Ligaments connect two or more bones and help stabilize joints. The present invention is concerned particularly with the posterior longitudinal ligament (PLL), which runs axially along the interior portion of the vertebral bodies and of the annulus fibrousus of the discs that lie between the vertebral bodies. The PLL protects the discs and imparts stability during flexion of the body [David W. L Hukins and Judith R. Meakin. Relationship between structure and mechanical function of the tissues of the intervertebral joint. Amer. Zool. 40 (2000):42-52]. Furthermore, nerves that innervate the PLL may participate in reflex loops that cause back muscles to stabilize the spine. Thus, neural receptors in the posterior longitudinal ligament, simultaneously with the output of the receptors from other ligaments such as the supraspinal ligament, as well as receptors in the discs, are thought to add their neural outputs to spinal interneurons, so as to reflexly activate the multifidus and longissimus muscles of the back in order to stabilize the spine in response to loads and movements [PANJABI M M. Clinical spinal instability and low back pain. J Electromyogr Kinesiol 13(4,2003):371-9].
The posterior longitudinal ligament may be injured (sprained, as a stretch and/or tear) as the result of sudden violent contraction, sudden torsion, lifting a heavy object, or other acute mechanical events. Because the PLL lies adjacent to the posterior annulus fibrosus of the intervertebral disc, inflammation of the disc that results from degeneration or herniation of the disc may secondarily contribute to dysfunction of the PLL, e.g., via inflammatory mediators. The most thoroughly investigated disease of the PLL itself is its ossification, which is more common in the cervical (70%), as compared to either thoracic (15%) or lumbar (15%) regions [Joji INAMASU, Bernard H. Guiot and Donald C. Sachs. Ossification of the Posterior Longitudinal Ligament: An Update on Its Biology, Epidemiology, and Natural History. Neurosurgery 58(6,2006): 1027-1039]. The PLL may also fold and compress a nerve root [BEATTY R A, Sugar O, Fox T A. Protrusion of the posterior longitudinal ligament simulating herniated lumbar intervertebral disc. J Neurol Neurosurg Psychiatry 31(1,1968):61-6].
Each vertebra is composed of the above-mentioned vertebral body (anteriorly) and an arch (posteriorly). Processes protrude from each arch and serve as points of attachment for muscles of the back. A spinous process protrudes backwards on each arch, and transverse processes extend from the lateral edges of each arch. The parts of the arch between the spinous and transverse processes are known as laminae, and the parts of the arch between the transverse processes and the body are known as pedicles. At the point where the laminae and pedicles meet, each vertebra contains two superior articular facets and two inferior articular facets. The pedicle of each vertebra is notched at its superior and inferior edges. Together the notches from two contiguous vertebra form an opening, the intervertebral neural foramen, through which spinal nerves pass.
A vertebral arch also contains an opening (the vertebral foramen) which forms a canal through which the spinal cord passes, protecting the spinal cord and nerve roots that exit from it. Because the spinal cord stops growing in infancy while the bones of the spine continue to grow, the spinal cord in adults ends at about the level of the vertebra L1/L2. Below that vertebral level, a bundle-like structure of nerve fibers, known as the cauda equina, occupy the vertebral foramen, which emanates from the terminus of the spinal cord (the conus medullaris). Thus, the lumbar vertebral foramen surrounds the spinal cord/conus medullaris above vertebrae L1/L2 and the cauda equina nerve roots below vertebrae L1/L2. [J. D. STEWART Cauda equina disorders. Chapter 6, pp 63-74. In: Neurologic Bladder, Bowel and Sexual Dysfunction (Clare J Fowler et al, eds) Amsterdam: Elsevier Science, 2001].
The above-mentioned structures are illustrated in FIGS. 1 to 4. Features shown in those figures that are particularly relevant to the present invention include the locations of the posterior longitudinal ligament (PLL) and the annulus fibrosus of the intervertebral disc(s) that lies adjacent to the PLL. For future reference, the location of electrodes of the present invention, which are implanted adjacent to the PLL, is also shown in FIGS. 1-4 (item 6 in FIG. 1, item 6 in FIG. 2, item 6 in FIG. 3, and within regions 50 and/or 51 in FIG. 4).
FIG. 1 shows the spine in a cross section perpendicular to its long axis, cut through one of the lumbar discs. The interconnections between the nerves that are shown in FIG. 1 are relevant to the mechanism by which the disclosed electrical stimulation of nerves innervating the PLL and annulus fibrosus may reduce back pain [EDGAR M A. The nerve supply of the lumbar intervertebral disc. J Bone Joint Surg Br 89(9,2007):1135-9]. Structures labeled in FIG. 1 are as follows: nucleus pulposus 1; annulus fibrosus 2; anterior longitudinal ligament 3; posterior longitudinal ligament 4; thecal sac 5; electrodes of the present invention situated in the anterior epidural space 6; filum terminale 7; intrathecal nerve root of the cauda equina 8; ventral nerve root 9; dorsal nerve root 10; dorsal root ganglion 11; dorsal ramus of the spinal nerve 12; medial branch of the dorsal ramus 13; sinuvertebral nerve (meningeal branch of the spinal nerve) 14; connecting sympathetic branch from gray ramus to sinuvertebral nerve 15; neural radicals from sinuvertebral nerve to disc 16; white ramus communicans 17; gray ramus communicans 18; sympathetic neural radicals to disc surface 19; paraspinal sympathetic ganglion 20; paraspinal sympathetic chain 21; anterior branch from sympathetic ganglion to disc surface 22; branches from sympathetic ganglion to disc surface 23; and posterior epidural space 24. FIG. 1 is adapted from: J. Randy JINKINS. The anatomic and physiologic basis of local, referred, and radiating lumbosacral pain syndromes related to disease of the spine. J Neuroradiol 31 (2004): 163-180.
FIG. 2 shows a section of the spine viewed from the side (left-to-right). The section is angled slightly away from the midline of the back, so as to demonstrate many of the ligaments of the spine. Vertebral bodies are labeled T12 through S1 as shown. Structures otherwise labeled in FIG. 2 are as follows: anterior longitudinal ligament 3; posterior longitudinal ligament 4; spinal cord 26; cauda equina 27; membrane of dura mater that surrounds the spinal cord and the cauda equina (thecal sac, dural tube) containing cerebral spinal fluid 5; electrodes of the present invention situated in anterior epidural space 6; posterior epidural space 24; anterior epidural space 25; intervertebral disc 29; ligamentum flavum 30; interspinous ligament 31; supraspinous ligament 32; sacrococcygeal ligament 33; and sacral hiatus 34.
FIG. 3 shows a posterior-to-anterior view of the lumbar spine, viewed obliquely on the left side of the patient. Vertebral bodies are labeled L3 through L5 as shown. Structures otherwise labeled in FIG. 3
are as follows: posterior longitudinal ligament 4; electrodes of the present invention situated in anterior epidural space 6; membrane of dura mater that surrounds the cauda equina (thecal sac, dural tube), containing cerebral spinal fluid 5; cauda equina nerve roots 27; intervertrbal disc 29; ligamentum flavum 30; L3 nerve root 35; L4 nerve root 36; L5 nerve root 37; pedicle (cut) 40; lamina (cut) 41; spinous process 42; transverse process 43; superior articular process 44; and facet joint 45.
The present invention electrically stimulates nerves in the PLL, the connective tissue between the PLL and annulus fibrosus and/or periosteum, and in the superficial layer of the dorsal aspect of the annulus fibrosus that lies under the PLL [BOGDUK N, Tynan W, Wilson A S. The nerve supply to the human lumbar intervertebral discs. J Anat 132(1,1981):39-56; EDGAR M A. The nerve supply of the lumbar intervertebral disc. J Bone Joint Surg Br 89(9,2007):1135-9; KOJIMA Y, Maeda T, Arai R, Shichikawa K. Nerve supply to the posterior longitudinal ligament and the intervertebral disc of the rat vertebral column as studied by acetylcholinesterase histochemistry. I. Distribution in the lumbar region. J Anat 169 (1990):237-46; J. H. MULLIGAN. The innervation of the ligaments attached to the bodies of the vertebrae. J Anat 91(4,1957): 455-465]. FIG. 4 shows a posterior-to-anterior view of the innervation of the posterior longitudinal ligament (PLL) and of the annulus fibrosus of the intervertebral disc that lies adjacent to the PLL. In this view, many of the structures shown in FIG. 3 are removed. Structures labeled in FIG. 4 are as follows: posterior longitudinal ligament 4; intervertebral fibers of the PLL 48; vertebral (longitudinal) fibers of the PLL 49; sinuvertebral nerve 14; nerve root 38; pedicle (cut) 40; horizontal region that may be stimulated by the disclosed devices 50; and vertical (longitudinal) region that may be stimulated by the disclosed devices 51.
Low back pain is extremely prevalent and is the second most common reason for patients to seek medical attention. Pain may be elicited during times of overexertion that results in sprain, strain, or spasm in one or more of the muscles or ligaments in the back. If the spine becomes overly strained or compressed, a disc may rupture or bulge outward. Prolonged stresses or degenerative changes facilitated by obesity, smoking, arthritis, poor posture, or unhealthy activity-related habits may result in injury to the intervertebral disc, resulting in chronic discogenic-mediated low back pain [Devon I RUBIN. Epidemiology and risk factors for spine pain. Neurol Clin 25 (2007): 353-371; MANCHIKANTI L, Singh V, Datta S, Cohen S P, Hirsch J A; American Society of Interventional Pain Physicians. Comprehensive review of epidemiology, scope, and impact of spinal pain. Pain Physician 12(4,2009):E35-70].
Acute back pain tends to come on suddenly, but also tends to improve in a short period of time with short-term conservative treatment, such as medication, exercise, physical therapy or rest [ATLAS S J, Deyo R A. Evaluating and managing acute low back pain in the primary care setting. J Gen Intern Med 16(2,2001):120-31]. Chronic back pain is commonly described as deep, aching, dull or burning pain in one area of the back, which may also travel down the leg(s). It tends to last a month or more or may be a persistent unrelenting problem. Sciatica is pain that begins in the hip and/or buttocks and travels down the back of the leg. There are many causes of chronic back pain, including some that are from intra-abdominal disorders that can cause pain to be referred to the back. Other examples of causes of back pain are as follows: A radiculopathy can be due to a pinched nerve resulting from a herniated disc; sciatica can be due to pinched nerves in vertebrae L4-S3; central spinal stenosis is due to narrowing of the spinal canal; foraminal stenosis is due to bone spurs that protrude into the neural foramen and put pressure on a nerve root; and low back pain can also be due to gradual loss of normal spinal structure associated with spondylosis, spinal osteoarthritis, and/or degenerative disc disease [Michael DEVEREAUX. Low back pain. Med Clin N America 93 (2009):477-501; Michelle LIN. Musculoskeletal Back Pain. Chapter 51, pp 591-603. In: Rosen's Emergency Medicine: Concepts and Clinical Practice, 7th edition (Marx J A, Hockberger R S, Walls R M, et al, eds). Philadelphia: Mosby Elsevier, 2009; LAST A R, Hulbert K. Chronic low back pain: evaluation and management. Am Fam Physician 79(12,2009):1067-74; McCAMEY K, Evans P. Low back pain. Prim Care 34(1,2007):71-82]. CHOU et al provide a flowchart to assist in the diagnosis and subsequent treatment of low back pain [CHOU R, Qaseem A, Snow V, Casey D, Cross J T Jr, Shekelle P, Owens D K; Clinical Efficacy Assessment Subcommittee of the American College of Physicians; American College of Physicians; American Pain Society Low Back Pain Guidelines Panel. Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Ann Intern Med 147(7,2007): 478-91].
The present invention is concerned primarily with back pain that is due to degenerative disc disease, wherein degenerative changes following loss of hydration of the nucleus pulposus lead to circumferential or radial tears within the annulus fibrosus. Annular tears within the outer annulus stimulate the ingrowth of blood vessels and accompanying nociceptors into the outer annulus, for example, from the overlying posterior longitudinal ligament. Nerve endings are recruited to the area of injury and sensitized by inflammatory cytokines and other chemofactors. Pain transmission is then sustained by chronic inflammation and exacerbated by constant axial loading [KALLEWAARD J W, Terheggen M A, Groen G J, Sluijter M E, Derby R, Kapural L, Mekhail N, van Kleef M. (15.) Discogenic low back pain. Pain Practice 10(6,2010):560-79; Keith D. WILLIAMS and Ashley L. Park. Lower Back Pain and Disorders of Intervertebral Discs. Chapter 39, pp. 2159-2236. In: Campbell's Operative Orthopaedics, 11th edition (S. Terry Canale and James H. Beatty, eds). Philadelphia: Mosby Elsevier, 2007; AUDETTE J F, Emenike E, Meleger A L. Neuropathic low back pain. Curr Pain Headache Rep 9(3,2005):168-77; HURRI H, Karppinen J. Discogenic pain. Pain 112(3,2004):225-8; FREEMONT A J, Peacock T E, Goupille P, Hoyland J A, O'Brien J, Jayson M I. Nerve ingrowth into diseased intervertebral disc in chronic back pain. Lancet 350(9072,1997):178-81].
Although the pathophysiology of degenerative disc disease is incompletely understood, it is thought that sensitization of these nociceptors by various inflammatory repair mechanisms may lead to chronic discogenic pain [MARTIN M D, Boxell C M, Malone D G. Pathophysiology of lumbar disc degeneration: a review of the literature. Neurosurg Focus 13(2,2002):Article 1, pp. 1-6; PENG B, Wu W, Hou S, Li P, Zhang C, Yang Y. The pathogenesis of discogenic low back pain. J Bone Joint Surg Br 87(1,2005): 62-7; Y. AOKI, K. Takahashi, S. Ohtori & H. Moriya: Neuropathology Of Discogenic Low Back Pain: A Review. The Internet Journal of Spine Surgery 2 (1,2005): 1-9; WALKER M H, Anderson D G. Molecular basis of intervertebral disc degeneration. Spine J 4(6 Suppl, 2004):1585-1665; BOSWELL M V, et al. Interventional techniques: evidence-based practice guidelines in the management of chronic spinal pain. Pain Physician 10(1,2007):7-111; J. Randy JINKINS. The anatomic and physiologic basis of local, referred, and radiating lumbosacral pain syndromes related to disease of the spine. J Neuroradiol 31 (2004): 163-180; SEAMAN D R, Cleveland C 3rd. Spinal pain syndromes: nociceptive, neuropathic, and psychologic mechanisms. J Manipulative Physiol Ther 22(7,1999):458-72; NAKAMURA S I, Takahashi K, Takahashi Y, Yamagata M, Moriya H. The afferent pathways of discogenic low-back pain. Evaluation of L2 spinal nerve infiltration. J Bone Joint Surg Br 78(4,1996):606-12; TAKEBAYASHI T, Cavanaugh J M, Kallakuri S, Chen C, Yamashita T. Sympathetic afferent units from lumbar intervertebral discs. J Bone Joint Surg Br 88(4,2006):554-7].
The current standard for diagnosing discogenic pain is pressure-controlled provocative discography [TOMECEK F J, Anthony C S, Boxell C, Warren J. Discography interpretation and techniques in the lumbar spine. Neurosurg Focus 13(2,2002):Article 13, pp 1-8; ZHANG Y G, Guo T M, Guo X, Wu S X. Clinical diagnosis for discogenic low back pain. Int J Biol Sci 5(7,2009):647-58]. Diagnostic nerve blockade may also be used to characterize the nerve source of the low back pain [MANCHIKANTI L, Singh V, Pampati V, Damron K S, Barnhill R C, Beyer C, Cash K A. Evaluation of the relative contributions of various structures in chronic low back pain. Pain Physician 4(4,2001):308-16].
Several therapies have been used to target the nociceptive nerve fibers within the affected discs in patients with discogenic back pain. Non-surgical techniques involve pain medication and physical therapy with behavioral modification [KINKADE S. Evaluation and treatment of acute low back pain. Am Fam Physician 75(8,2007):1181-8; Brian S WILLIAMS and Paul J Christo. Pharmacological and interventional treatments for neuropathic pain. Chapter 12, pp 295-375. In: Mechanisms of Pain in Peripheral Neuropathy (M Dobretsov and J-M Zhang, eds). Trivandrum, India: Research Signpost, 2009; CHOU R, Huffman L H; American Pain Society; American College of Physicians. Nonpharmacologic therapies for acute and chronic low back pain: a review of the evidence for an American Pain Society/American College of Physicians clinical practice guideline. Ann Intern Med 147(7,2007): 492-504].
Other destructive minimally invasive and surgical techniques have been used when conservative measures fail [BOSWELL M V, et al. Interventional techniques: evidence-based practice guidelines in the management of chronic spinal pain. Pain Physician 10(1,2007):7-111; LAVELLE W F, Lavelle E D, Smith H S. Interventional techniques for back pain. Clin Geriatr Med 24(2,2008):345-68]. Minimally invasive techniques include Intradiscal electrothermal therapy (IDET), which involves the application of heat via a needle that is inserted transcutaneously into the disc [DERBY R, Eek B, Chen Y, O′neill C, Ryan D. Intradiscal Electrothermal Annuloplasty (IDET): A Novel Approach for Treating Chronic Discogenic Back Pain. Neuromodulation 3(2,2000):82-8]. Alternatively, radiofrequency annuloplasty is a technique used to target the affected area using a needle to deliver radiofrequency energy for destructive purposes [HELM S, Hayek S M, Benyamin R M, Manchikanti L. Systematic review of the effectiveness of thermal annular procedures in treating discogenic low back pain. Pain Physician 12(1,2009):207-32]. Rather than using heat to destroy nerves in the affected area, it has been proposed that they may be destroyed using ionizing radiation [U.S. Pat. No. 7,634,307, entitled Method and apparatus for treatment of discogenic pain, to SWEENEY].
Surgical techniques are also used to remove a large portion of the disc followed by a fusion procedure between the two adjoining vertebral bodies [CHOU R, Baisden J, Carragee E J, Resnick D K, Shaffer W O, Loeser J D. Surgery for low back pain: a review of the evidence for an American Pain Society Clinical Practice Guideline. Spine 34(10,2009):1094-109; LAVELLE W, Carl A, Lavelle E D. Invasive and minimally invasive surgical techniques for back pain conditions. Med Clin North Am 91(2,2007):287-98; SCHWENDER J D, Foley K T, Holly L T, Transfeldt, E E. Minimally Invasive Posterior Surgical Approaches to the Lumbar Spine. Chapter 21, pp. 333-341 In: The Spine, Fifth Edition (Harry N. Herkowitz, Richard A. Balderston, Steven R. Garfin, Frank J. Eismont, eds). Philadelphia: Saunders/Elsevier, 2006; GRIFFITH S L, Davis R J, Hutton W C. Repair of the Anulus Fibrosus of the Lumbar Disc. Chapter 12 (pp 41-48), In: Nucleus Arthroplasty Technology in Spinal Care: Volume II-Biomechanics & Development. Davis R, Cammisa F P, Girardi F P, Hutton W C, Editors. Bloomington, M N: Raymedica Co, 2007].
As described in the above-cited publications, all of these techniques have varying degrees of success, and pain relief is generally temporary. A problem with IDET and similar minimally invasive techniques is that destruction of nociceptors within the posterior annulus is variable and incomplete. In addition, the offending region involving the PLL is not addressed.
Several patents or patent applications disclose methods similar to radiofrequency annuloplasty, wherein an array of electrodes (a lead) is introduced into the disc (but not into the epidural space adjacent to the disc) to thermally ablate disc tissue. In U.S. Pat. No. 8,066,702, entitled Combination electrical stimulating and infusion medical device and method, to RITTMAN, III, et al., radiofrequency energy is transmitted to tissue surrounding the lead, thereby ablating the tissue. U.S. Pat. No. 6,772,012 and U.S. Pat. No. 7,270,659, entitled Methods for electrosurgical treatment of spinal tissue, to RICART et al., also describe controlled heating to ablate various tissues in or around the vertebral column using a radiofrequency voltage, including possibly a posterior longitudinal ligament. A thermal ablation method that may also be directed to the posterior longitudinal ligament, involving electrosurgically coagulating nerve tissue within the posterior of the annulus fibrosus by applying heat, is disclosed in U.S. Pat. No. 7,331,956, entitled Methods and apparatus for treating back pain, to HOVDA et al. Similarly, abandoned application U.S. Ser. No. 11/105,274, corresponding to publication No. US20050261754, entitled Methods and apparatus for treating back pain, to WOLOSZKO et al., describes denervation of an intervertebral disc or a region of the posterior longitudinal ligament by the controlled application of heat to a target tissue. All of the methods disclosed in those patents affect the offending region irreversibly, through the application of joule heating. In contrast, in the preferred embodiments of the present invention, electrodes are introduced to affect the offending region reversibly, not irreversibly. Alternatively, in another embodiment of the present invention, the offending region may be affected irreversibly, but in contrast to the above-mentioned patents, the irreversible damage is not due to joule heating.
Lower back pain has been treated reversibly by stimulation of the spinal cord, using electrical stimulation devices that are used generically to modulate neuronal function [ten VAARWERK I A, Staal M J. Spinal cord stimulation in chronic pain syndromes. Spinal Cord 36(10,1998):671-82; NORTH R B, Wetzel F T. Spinal cord stimulation for chronic pain of spinal origin: a valuable long-term solution. Spine 27(2,2002):2584-91; STOJANOVIC M P, Abdi S. Spinal cord stimulation. Pain Physician 5(2,2002):156-66; BAROLAT G, Sharan A. Spinal Cord Stimulation for Chronic Pain Management. In Pain Management for the Neurosurgeon: Part 2, Seminars in Neurosurgery 15 (2,2004):151-175; R. B. NORTH. Neural interface devices: spinal cord stimulation technology. Proceedings of the IEEE 96(7,2008): 1108-1119; Allen W. BURTON, Phillip C. Phan. Spinal Cord Stimulation for Pain Management. Chapter 7, pp. 7-1 to 7-16, In: Neuroengineering (Daniel J. DiLorenzo and Joseph D. Bronzino, eds). Boca Raton: CRC Press, 2008; Steven FALOWSKI, Amanda Celii, and Ashwini Sharan. Spinal cord stimulation: an update. Neurotherapeutics 5(1,2008):86-99; KUNNUMPURATH S, Srinivasagopalan R, Vadivelu N. Spinal cord stimulation: principles of past, present and future practice: a review. J Clin Monit Comput 23(5,2009):333-9]. Other examples of electrical stimulation are deep brain stimulation for treatment of Parkinson's disease or other movement disorders, complex regional pain syndrome (previously referred to as reflex sympathetic dystrophy), post herpetic neuralgia and others. In addition to centrally mediated nerve stimulation, peripheral nerve stimulation has also been used to successfully treat neuropathic pain syndromes such as occipital, trigeminal, and post herpetic neuralgias [WHITE P F, Li S, Chiu J W. Electroanalgesia: its role in acute and chronic pain management. Anesth Analg 92(2,2001):505-13; STANTON-HICKS M, Salamon J. Stimulation of the central and peripheral nervous system for the control of pain. J Clin Neurophysiol 14(1,1997):46-62].
Although spinal cord electrical stimulation is an established method for treating axial lower back pain, it produces improvement in back pain in only approximately 50% of patients [John C. OAKLEY. Spinal Cord Stimulation in Axial Low Back Pain: Solving the Dilemma. Pain Medicine 7 (Supplement s1,2006):558-563]. The devices used for spinal cord stimulation comprise: (1) electrodes that are implanted in the spine, and (2) a power source that delivers electrical pulses to the electrodes. The present invention also discloses electrodes that are implanted in the spine and a power source that powers the electrical pulses that are delivered to the electrodes.
Commercially available general-purpose electrodes and pulse generators that are used for spinal cord stimulation and peripheral nerve stimulation could in principle also be used to electrically stimulate the lumbar posterior longitudinal ligament and adjoining outer posterior annulus fibrosus of the intervertebral discs. However, as disclosed below, such general-purpose stimulators are not well-suited for the objectives of the present invention. Furthermore, devices according to the present invention are not spinal cord stimulators for treating back pain. In fact, electrodes in the present invention are placed in the canal defined by the vertebral foramen in the lumbar region and in most cases, below the spinal cord, where the cauda equina rather than the spinal cord occupies that opening. Heretofore, when the lumbar columns have been stimulated with spinal cord stimulator devices, it has been for purposes of spasticity control or the generation of muscle activity in spinal cord injury patients, not for purposes of treating back pain [DANNER S M, Hofstoetter U S, Ladenbauer J, Rattay F, Minassian K. Can the human lumbar posterior columns be stimulated by transcutaneous spinal cord stimulation? A modeling study. Artif Organs 35(3,2011):257-62]. In order to explain differences between the present invention and spinal cord stimulators, the development and use of spinal cord stimulators will first be summarized.
Spinal cord electrical stimulation for the treatment of pain was first performed in 1967 by SHEALY and colleagues [SHEALY C N, Mortimer J T, Reswick J B. Electrical inhibition of pain by stimulation of the dorsal columns: preliminary clinical report. Anesth Analg 46(4,1967):489-91]. In the decade that followed, many variations in technique were tried. Electrodes were implanted at different locations relative to the spinal cord: in endodural, subdural, subarachnoid, and epidural positions. To do so, a significant amount of spinal bone was often removed, in order to allow placement of the electrodes (a surgical laminectomy, or complete removal of vertebral lamina). In other cases, a small window of bone was drilled over the area, using less invasive techniques (laminotomy, or partial removal of vertebral lamina). Finally, minimally invasive techniques were developed to implant a catheter-like electrode lead percutaneously.
Rather than implanting the electrodes one-by-one, leads (also known as electrode arrays) were developed wherein multiple electrodes were mounted on, in, or about an insulating substrate, and the lead was then implanted. Such leads may have the shape of a plate and are said to contain paddle electrodes, plate electrodes, ribbon electrodes, surgical electrodes or laminotomy electrodes. For percutaneous implantation, the leads may also have the shape of a wire or catheter, which are said to contain percutaneous or wire electrodes.
In almost all cases, the electrodes were implanted on the posterior side of the spinal cord, i.e., the side most accessible from the back. However, in 1975 LARSON et al. and HOPPERSTEIN implanted electrodes on the anterior side of the spinal column, in an attempt to improve the low success rate of spinal cord stimulation in reducing pain [Sanford J. LARSON, Anthony Sances, Joseph F. Cusick, Glenn A. Meyer, Thomas Swiontek. A comparison between anterior and posterior spinal implant systems. Surg. Neurol. 4 (1975):180-186; Reuben HOPPENSTEIN. Electrical stimulation of the ventral and dorsal columns of the spinal cord for relief of chronic intractable pain: preliminary report. Surg. Neurol. 4 (1975):187-194]. In contrast to the present invention, though, they did not implant the anterior electrodes within the anterior epidural space, they did not attempt to implant electrodes in the lumbar spine, and they were not concerned with the treatment of back pain. Furthermore, the anteriorly-placed electrodes were configured to stimulate the spinal cord, which is different than the configuration that would stimulate only nerves in the posterior longitudinal ligament and the underlying annulus fibrosus as in the present invention.
The anterior location of the electrode in the epidural space is particularly relevant to the present invention. The epidural space is the space within the spinal canal lying outside the dura mater (dural or thecal sac), which contains lymphatics, spinal nerve roots, loose fatty tissue, small arteries, and blood vessels. The epidural space surrounds the dural sac and is bounded by the posterior longitudinal ligament anteriorly, the ligamenta flava and the periosteum of the laminae posteriorly, and the pedicles of the spinal column and the intervertebral neural foramina containing their neural elements laterally. The space communicates freely with the paravertebral space through the intervertebral neural foramina. For spinal cord stimulation, the electrodes are now invariably implanted in the posterior epidural space.
However, a percutaneous lead may be accidentally introduced into the anterior epidural space, which is considered to be an error, and the lead is withdrawn. Thus, FALOWSKI et al. write that “Frequently, the electrode curves around the dural sac and ends in the ventral epidural space. A gentle lateral curve of the electrode shortly after its entry into the epidural space should arouse the suspicion that it is directing ventrally around the dural sac. Absolute confirmation of the ventral location arises from the stimulation generating violent motor contractions or observation [by fluoroscopy] in the lateral plane which would readily disclose the anterior position of the electrode tip.” [Steven FALOWSKI, Amanda Celii, and Ashwini Sharan. Spinal cord stimulation: an update. Neurotherapeutics 5(1,2008):86-99]. Thus, in contrast to the present invention, implantation of a spinal cord electrode in the anterior epidural space is considered to be an error, and in any event, the implantation of spinal cord stimulator electrodes is not performed in the lumbar spine (e.g., L3-L5). Furthermore, in the present invention, the electrical stimulus is directed towards the posterior longitudinal ligament in such a way that motor contractions are not induced by the stimulation. Applicant is unaware of the deliberate percutaneous implantation of a spinal cord stimulator in the anterior epidural space. As disclosed herein, such deliberate implantation in the anterior epidural space would likely involve a different anatomical route than the interlaminal approach that is taken for access to the posterior epidural space. Thus, as is known from the methods for performing epidural injections, to reach the anterior epidural space, a transforaminal anatomical approach may be taken, and for lumbar vertebrae, a sacral route may be taken as well [Mark A. HARRAST. Epidural steroid injections for lumbar spinal stenosis. Curr Rev Musculoskelet Med 1:(2008):32-38].
Spinal cord stimulation is performed for the treatment of back pain, but it involves stimulation in vertebrae other than the lumbar spine L3-L5. The vertebral location of the stimulator electrodes is selected on the basis of the location of the patient's pain. BAROLAT et al. mapped the body areas that may be targeted by stimulation of the spinal cord in different vertebrae and made the following observations concerning how best to stimulate to treat lower back pain. “It is very difficult to stimulate the low back only, without intervening chest/abdominal wall stimulation . . . (1) the peak curve for low-back stimulation coincides with the peak curve for the chest/abdominal wall . . . (2) the chest/abdominal wall region has a higher percentage of stimulation than the low back; and (3) the chest/abdominal wall area has a lower stimulation threshold than the low back. All of these factors contribute to the challenge of being able to direct stimulation selectively to the low back without interference from the body walls. In our experience, the best location was about T9-10, with the electrode placed strictly at the midline.” [BAROLAT G, Massaro F, He J, Zeme S, Ketcik B. Mapping of sensory responses to epidural stimulation of the intraspinal neural structures in man. J Neurosurg 78(2,1993):233-9].
It is therefore not surprising that the effectiveness of spinal cord stimulation for lower back pain is equivocal. Most reviews of its effectiveness have been made in connection with the treatment of Failed Back Surgery Syndrome (FBSS), which may involve pain in locations in addition to the back (e.g., the leg). A Cochrane review of random clinical trials for the treatment of FBSS by spinal cord stimulation concluded that although one clinical trial does provide some limited evidence in favor of spinal cord stimulation, the numbers are small and as a result the study fails to achieve statistical significance [MAILIS_GAGNON A, Furlan A D, Sandoval J A, Taylor R. Spinal cord stimulation for chronic pain. Cochrane Database Syst Rev. 2004; (3):CD003783, updated 2009]. Other reviews indicate that up to 40 percent of such FBSS patients do not benefit substantially from spinal cord stimulation [ELDABE S, Kumar K, Buchser E, Taylor R S. An analysis of the components of pain, function, and health-related quality of life in patients with failed back surgery syndrome treated with spinal cord stimulation or conventional medical management. Neuromodulation 13(3,2010):201-9; FREY M E, Manchikanti L, Benyamin R M, Schultz D M, Smith H S, Cohen S P. Spinal cord stimulation for patients with failed back surgery syndrome: a systematic review. Pain Physician 12(2,2009):379-97].
Similarly, a review found that spinal cord stimulation for treatment specifically of discogenic pain might be useful, as evidenced by a reduction in opioid usage by such patients, but the review involved only a small number of patients [VALLEJO R, Manuel Zevallos L, Lowe J, Benyamin R. Is Spinal Cord Stimulation an Effective Treatment Option for Discogenic Pain? Pain Pract. 2011 Jul. 29. doi: 10.1111/j.1533-2500.2011.00489.x. (Epub ahead of print)]. OAKLEY reviews the problem of why approximately 50% of patients with lower back pain are not helped by spinal cord stimulation. He suggests that advances in stimulator technology may help, such as properly selecting the number and location of stimulator electrodes, using pulse generators with independent current control over each lead contact electrode, and optimizing the stimulation waveform (e.g., pulse width) [John C. OAKLEY. Spinal Cord Stimulation in Axial Low Back Pain: Solving the Dilemma. Pain Medicine 7 (Supplement s1,2006):S58-S63]. In regards to stimulus waveform optimization, AL-KAISY et al. suggest that the use of high frequency pulses may help [Adnan AL-KAISY, Iris Smet, and Jean-Pierre Van Buyten. Analgesia of axial low back pain with novel spinal neuromodulation. Poster presentation #202 at the 2011 meeting of The American Academy of Pain Medicine, held in National Harbor, Md., Mar. 24-27, 2011].
The above-cited literature demonstrates that the treatment of lower back pain by invasive electrical stimulation is in need of improvement. To that end, the present invention is motivated by the fact that the innervation of the posterior longitudinal ligament and the underlying annulus fibrosus may be the predominant origin of the lower back pain. Thus, KUSLICH et al. write that “ . . . we had the opportunity to perform more than 700 operations on the lumbar spine while using local anesthesia . . . . Back pain could be produced by stimulation of several lumbar tissues, but by far, the most common tissue of origin [of back pain] was the outer layer of the annulus fibrosus and posterior longitudinal ligament.” [KUSLICH S D, Ulstrom C L, Michael C J. The tissue origin of low back pain and sciatica: a report of pain response to tissue stimulation during operations on the lumbar spine using local anesthesia. Orthop Clin North Am 22(2,1991):181-7].
To affect the innervation of the lumbar posterior longitudinal ligament, the electrodes that stimulate them need to be placed in the lumbar spine, which is not done in spinal cord stimulation for back pain. At that lumbar location, the cauda equina is situated posterior to the posterior longitudinal ligament. Placement of an electrode between the posterior longitudinal ligament and the cauda equina would cause the cauda equina to be stimulated, if the electrode were to stimulate in all directions. Such stimulation of the cauda equina would be very undesirable because it would cause leg movements resulting from stimulation of nerve roots within the cauda equina.
In fact, there are only a few reasons for electrically stimulating the cauda equina, and they are not relevant to the treatment of discogenic back pain. Electrical stimulation of the cauda equina, through high voltage percutaneous or transcutaneous stimulation above the lumbar vertebrae, is sometimes done in order to assess conduction in the cauda equina, which is accompanied by electromyographic activity in muscles of a lower limb. However, this does not involve placement of an electrode in the epidural space [Maertens de NOORDHOUT A, Rothwell J C, Thompson P D, Day B L, Marsden C D. Percutaneous electrical stimulation of lumbosacral roots in man. J Neurol Neurosurg Psychiatry 51(2,1988):174-81]. Electrodes have been placed in the posterior epidural space in the vicinity of the conus medullaris and cauda equina, but this is done only for purposes of mapping or monitoring, not for the treatment of lower back pain, and not for purposes of stimulating the posterior longitudinal ligament or posterior annulus fibrosus [KOTHBAUER K F, Deletis V. Intraoperative neurophysiology of the conus medullaris and cauda equina. Childs Nery Syst 26(2,2010):247-53]. In another situation, a special electrode is used to enable restoration of at least partial control over lower-body functions that are directed by nerves emerging from the end of the spinal cord. The electrode is designed for introduction into the lower end of the dura beneath the conus of the spinal cord, to float in the intrathecal space that is loosely occupied by the sacral roots and other nerves of the cauda equina. Thus, that electrode is not implanted in the epidural space, and it is not intended to treat lower back pain or stimulate the posterior longitudinal ligament or posterior annulus fibrosus [U.S. Pat. No. 4,633,889, entitled Stimulation of cauda-equina spinal nerves, to TALALLA et al].
Therefore, if one wishes to electrically stimulate the lumbar posterior longitudinal ligament to treat back pain reversibly, but avoid stimulation of other structures adjoining the anterior epidural space, at least two problems must be addressed. One is that the electrical stimulation must be directed specifically to the posterior longitudinal ligament and its underlying structures, and this involves not only designing an asymmetric structure for the lead, but also the design of directionality of its insertion into the patient. A second problem is that electrodes, particularly percutaneous electrodes (wire, or catheter-like electrodes) have a tendency to migrate or rotate, such that even if the electrode were initially directed to stimulate the posterior longitudinal ligament, it may eventually rotate or migrate, thereby accidentally stimulating other tissues. The present invention is designed to address both of these problems. It also addresses the problem of selectively ablating the nerves if the reversible stimulation does not work.
These problems are not addressed in the patents that are related to the present invention. In U.S. Pat. No. 7,069,083, U.S. Pat. No. 7,831,306, and U.S. Pat. No. 8,086,317, all entitled System and method for electrical stimulation of the intervertebral disc, to FINCH et al., a percutaneous (wire, or catheter) lead is placed in a disc or just outside the outer confines of the disc, circumferentially along the entire perimeter of the annulus of the disc. The lead is not placed in the anterior epidural space, there is no suggestion of stimulating the posterior longitudinal ligament, the electrodes do not stimulate in a particular direction, and there is no suggestion of how rotational migration of its cylindrical lead might be retarded. In U.S. Pat. No. 7,945,331, entitled Combination electrical stimulating and infusion medical device and method, to VILIMS, it is suggested incidentally that his disclosed percutaneous (wire, or catheter) lead “is well suited for treatment of other areas along the spine to include the ventral canal along the posterior longitudinal ligament, ventral dura, and the posterior aspect of the disc.” However, there is no suggestion as to how the lead would be inserted or used in those locations. In one embodiment of that invention, “the electrodes are not formed circumferentially around the distal portion, but are formed more linearly along one side of the stimulation lead.” However, that patent does not suggest how such an electrode would be inserted to selectively stimulate any particular tissue, and it does not suggest how subsequent rotational migration of its cylindrical lead could be retarded. Furthermore, that patent is concerned with managing sacroiliac joint pain in a sacrum of a patient, not discogenic lumbar pain. None of the above-cited patents disclose devices that would almost completely cover a pain-generating region, such as the entire innervation of an offending lumbar posterior longitudinal ligament and adjacent posterior annulus fibrosus of the intervertebral disc(s).
In view of the foregoing, there is a need for a lumbar vertebral column electrical stimulator lead that is adapted for directional insertion into the anterior epidural space adjacent to the posterior longitudinal ligament; that will provide adjustable and reversible non-destructive modulation of nerves in the posterior longitudinal ligament and underlying annulus fibrosus to effectively reduce back pain, when connected to a pulse generator; that will cover the pain-generating region; that will stimulate only the posterior longitudinal ligament and underlying annulus fibrosus, but not nearby tissue such as the cauda equina or nerve roots; that is not susceptible to accidental rotation or migration; and that as a last resort may be used to irreversibly damage the offending nerves, without the use of thermal ablation that indiscriminately damages material near the offending nerves, such as collagen in the posterior longitudinal ligament.